Air compressor



Dec. 4, 1956 G. COTTER 2,772,831

AIR COMPRESSOR F-iled Feb. 16, 1955 IN V EN TOR.

George L. Coffer ATTO/QNEY ited ate atenrO house Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania 7 Applicationl 'ebruaryfi, 1953, Serial No. 337,141 4 Claims, or. 230-211 '4 This-invention relates to air compressors and more particularly to means 'for controlling the operating temperature thereof. R In the-operation of air compressors, excessive discharge temperatures, resultant from heat of compression of the air, tend to damage or otherwise cause faulty operation of the discharge valve mechanism either as a direct result oflsuch heat or as an-indirect result of carbonized oil deposits, in view of which, it is a prime object of the invention to provide a means and method whereby the temperature of operation of an air compressor may be reduced from that otherwise obtained. i j Another object of the invention is to provide an air compressor capable-of operating at higher discharge pressures than normally practical without excessive heating. Other objects and advantages will become apparent from the following more detailed description of the invention. Inthe accompanying drawing, the single figure is a schematic viewlof anair compressing system including an air compressor constructed in accordance, with a preferred form of the invention.

Description U ,Referring to-the drawing, the air compressor embodying the invention, and. designated by reference number 1, is disposed in a system' includinga storage reservoir 2, and aftercooler coils 3.. g 1 For the purpose'of illustration, the aircompressor 1 comprises a cylinder casing 4 having the usual piston 5 reciprocable therein in sliding sealing engagement with theusual inner cylinder wall 6 formed in' the casing. In the well-known manner, the piston 5 serves as a movable abutment defining one end of the usual cylinder chamber 7,' the opposite-end of which chamber 7 is closed by a pressure head 8 containing the usual inlet and discharge valves 9 and 10, respectively, which control admission of free air to and discharge of compressed air from the cylinder chamber7, respectively; inlet valve 9 being arranged for cooperation with a valve seat 11 to control communication between an inlet port 12 in pressure head 8 and the cylinder chamber 7 via an inlet chamber 13, constantly connected to port 12, and a bore 14 in which a fluted stem 14a attached to inlet valve 9 is slidably guided; and exhaust valve being disposed in a discharge chamber 15 and arranged for cooperation with a valve seat 16 to control 'communication between a discharge port 17 and the'cylinder chamber 7, by way of the chamber 15 and a port 18. A light compression spring 19, disposed in the inlet chamber 13 is arranged to cooperate with the fluted stem 14:: to bias the inlet valve 9 toward its seated position, in which it is shown in the drawing, closing bif the cylinder chamber 7 from the inlet port 12, and a similar light compression spring 20, disposed in the discharge chamber 15 is arranged to bias the discharge valve 10 toward its seated position, in which it is shown in the drawing, closing off the cylinder chamber 7 from the discharge port 17.

In the well-known manner, movement of the piston 5 {Patented Dec. 4, 1956 through its suction stroke from top dead center position in proximity of the pressure head 8 to bottom dead center position in which it is. shown in the drawing, will cause a suction in cylinder chamber'7 which causes the unseating of inlet valve 9 and admission of air from the atmosphere into, said chamber7 via inlet port 12, inlet chamber 13, bore 14, and the unseated inlet valve. Subsequent movement of the piston 9 through its compression stroke in the opposite direction, that is, from its bottom dead center position to its top dead center position, will cause compression of the air in chamber 7 and displacement of such air therefrom via port 18, discharge chamber 15, and port .17 by unseating of the discharge valve 10 against opposition of reservoir 2 pressure as experienced in discharge chamber' 15 and of the light bias spring 20. a i

The air compressor 1 further comprises the usual connecting rod 26 which operably connects, via a pin 27, the piston 5 to the usual crank shaft28 suitably driven by means (not shown) to cause reciprocating movement of the piston in the well-known manner.

The inlet port 12 is constantly open to the atmosphere and the discharge port 17 is constantly connected to the reservoir 2 via the aftercooler coils 3 which cool the compressed air discharged from the compressor enroute to the reservoir.

According to the invention, means are provided inthe compressor 1 for effecting admittance of cooled compressed air from the reservoir 2 into cylinder chamber. 7', during each successive compression stroke of the piston 5, for cooling purposes in order to limit the operating temperature of the compressor, in manner as hereinafter described.

Such means, as above referred to, may comprise a second inlet chamber 30, preferably formed within a portion of the casing 4, in constantlyopen communication with the reservoir 2 via such as a pipe 31a; anauxiliary air inlet passage 31, which may be formed in the pressure head 8, opening into the upper end of the cylinder chamber 7; an auxiliary-air-admission-controlling inlet valve 32 interposed between chamber 30 and chamber 31 in'cooperation with a seat 33 to control communication between said chambers; a valve stem 33a attached at one end to valve 32 and slidably guided within a suitable opening 34 in the casing 4 for reciprocably. moving the valve 32'into and out of engagement with its seat 33; a compression spring 35 encircling the stem 33a, in abut.- ment at its one end with an accommodating portion of the casing 4 and in abutment at its opposite end with a. collar element 36 suitably attached to the valve stem 33a, to urge said stem in the direction for causing engagement of the attached valve 32 with its seat 33; a pin 37, slidably disposed in a suitable casing opening 38 and extending into the interior of the crankcase portion 39 of the compressor device, adapted at its outermost end for engagement with the free end of thevalve stern 33a; a pivotally mounted finger 40 disposed within crankcase portion 39 in operative engagement with the innermost end of the pin 37; a cam 41 also disposed within crankcase portion 39 in operative engagement with the finger 40; a cam shaft 42 secured through the medium of such as a set screw 42a to rotate'the cam 41; andintermeshing gears 43 and 44 secured to rotate with the cam shaft 42 and compressor crankshaft 28 to cause rotation of the former with respect to the latter.

Operation According to the invention, during each compression stroke of the piston 5, the valve 32 is unseated for a portion of such stroke by action of the crankshaft rotated cam 41 through the medium of the valve stem 33a, pin 37 and finger 40 to allow cooled compressed air from .inch, for. example.

the vreservoir '2 to flow via pipe 31a into the cylinder Chamber 7 to mix with the initial char-gerof air therein admitted from the atmosphere past inlet valve 9 during the suction stroke of the piston for purposes of reducing ithe temperature of .the'air discharged from such 'Cylinderchamber past discharge valve 10.

It-isintended that the compressor 1 be employed in conjunction with the :usual automatic means (not shown) for controlling operation of such compressor, by startingland stopping .or loading and unloading, to maintain pressure of air-in the reservoir 2 within a selected range between upper and lower limits,.such as one hundred pounds per square inch and ninety pounds per square Under such conditions of operation, the profile of the-cam 41 and its angular position with respect to shaft 42 are selected such that, following opening of valve 32 during .each successive compres: s'iongstroke of the piston 5 to permit entrance of compressed. air. from reservoir .2 into cylinder chamber 7, the spring 35 will be permitted to close said valve 32 before the pressure of the air. in cylinder chamber 7 attains a value greaterv than that maintained in reservoir 2, to thus prevent air compressed in cylinder. chamber 7 from flowing .to the reservoir 2 via pipe 31a. This assures that the air. compressed in cylinder chamber 7 will bedischarged :to the reservoir 2 exclusively by way .of the discharge valve 10 and cooler coils 3 as the pressure of air in cylinder chamber 7 is increased to a value abovethe pressure in the reservoir during completion of each compression stroke of the piston following closure of the valve .32.

It should be pointed outthat, for any given discharge pressure, the additional work necessary to drive the compressor. 1 as a result of such cooling air admittance in the novel compressor system, as well as the cooling effect produced by the admission of the compressed air to the chamber 7 during the compression stroke of piston 5 in manner as described, both depend upon the during movement .of piston 5 in its compression stroke.

It has been found by test that a certain single-cylinder compressor of a particular size, operating at a particular speed and at a discharge pressure of 150. pounds per square inch, for example, for a tolerable increase in work input .to such-compressor might realize maximum cooling effect by opening. of the'valve 32 at :the time that the piston 5 has completed substantially half of its compression stroke; the discharge temperature under such conditions being. in the vicinity of 370 F., approximately two hundred degrees less than a prohibitive temperature that would otherwise prevail were the compressionof the initial charge from atmospheric pressure to 150 p. s. i. performed by piston 5 without admittance of cooling air into chamber. 7. At a discharge pressure of p. s. i., it was found that desired cooling input to the compressor. might .be realized by unseating of valve 32 at a time closer to the beginning of the compression stroke.

Accordingly, therefore, in keeping with another feature of the invention, by provision of means such as the set screw 42a, the cam 41 may be adjusted to different angular. positions on the cam shaft 42 to attain the desired opening time ofthe valve 32 with respect to operation of piston 5 for any given discharge pressure of the com: pressor.

Summary From the foregoing, it will be apparent that I have provided an air compressor, incorporating improved cool- 4 V ing air admittance control means, which is capable of operating .at relatively high discharge pressures,.in the neighborhood of p. s. i., for example, without excessive heating.

In operation of the novel compressor, the usual charge of atmospheric air is drawn into the compressor cylinder during each successive suction stroke of the compressor piston and such charge compressed and discharged during each successive compression stroke of the compressor a ston- The p sed air t us charged from he compressor is cooled and fed into the usual storage reservoir for use, and, according to the invention, for a certain interval during each successive compression stroke of the compressor piston, a portion of the cooled compressed air from the storage reservoir is admitted into the cylinder for cooling purposes.

Having now described my invention, what I claim as new and desire to secure by Letters Patent, is:

1. 'In combination with alsource of cooled gas under pressure, a compressor having a .gas compressing chamber and piston means defining an end wall of said chamber movable alternately and successively through :a suction stroke in which said chamber is expanded from a minimum size and through a compression stroke in which said chamber is contracted from a maximum size to its minimum size, a rotatable crankshaft operatively connected to said piston means, pressure differential operated inlet valve means connected to said chamber and responsive to reduction in pressure of gas in said chamber resultant from movement of said piston means through its suction stroke to open said chamber for admission thereto of an initial charge of gas to be com.- pressed, cooling-gas-admission-control valve means connected to said chamber and to said source for controlling admission of gas under pressure from said source into said chamber, bias means connected to and urging'said cooling-gas-admission-control valve means towards a. closed position, and cam means operatively connected to said cooling-gas-admission-control valve means and connected to said crankshaft for rotation in synchronism therewith to open said cooling-gas-admission-control valve means for a period during the compression stroke of said piston means and permitting said cooling-gasadrnission-control valve means to be closed by said bias means at all other times.

2. The combination as set forth in claim 1, including compressor dischargecontrol valve means connected to the compressor, and conduit means connected to said discharge valve means and to said source for delivering gas under pressure from said gas compressing chamber to said source.

3. The combination as set forth in claim 2, wherein means is included for cooling the gas in said conduit means.

4. The combination as set forth, in claim 1, including manual means for adjusting the position of said cam means relative to said crankshaft to change the timing of admission of cooled gas under pressure by said coolinggas-admission-control valve means from said source to said chamber during the compression stroke of said piston means.

References Cited in the file of this patent U ED- AT S. PATENTS.

Great Britain Ian. 30, 1928 

